1. Field of the Invention
The present invention relates to an image reading apparatus such as a scanner or the like that illuminates a document using a plurality of point light sources arrayed at a predetermined interval to thereby read a document image, and to an image forming apparatus such as a copying machine, facsimile, multifunction peripheral, and the like provided with this type of image reading apparatus.
2. Related Art
Conventionally, an image reading apparatus for reading image information from a document, such as scanner, is known that illuminates light from an illumination means onto the document, images reflected light from the document, and converts the resulting image information into a digital electrical signal using a photoelectric conversion means such as a CCD image sensor, or the like.
In this type of image reading device, a general purpose xenon lamp or a cold cathode tube, or the like is known as an illumination means that illuminates light onto the document.
In recent years, in substitution for the above, a plurality of low cost, durable, and high luminance point light sources such as a LED (light-emitting diode) is arrayed at a predetermined interval along a main scanning direction (for example, a LED array substrate) as an illumination means.
In an image reading apparatus that uses an illumination means that arrays a plurality of point light sources (LED) such as an LED array substrate, a light guide member formed from a translucent resin, glass, or the like is disposed for example between a plurality of LEDs and a document to guide light emitted from the LEDs onto the document surface. This light guide member suppresses a non-uniform distribution in illumination on the document surface by guiding light that is emitted from the LED and dispersed into a conical shape along the main scanning direction to thereby illuminate the document.
However, when there is a deviation in the positional relationship between the light guide member and the plurality of LEDs, it is sometimes the case that light cannot be uniformly illuminated with respect to the main scanning direction of the document.
In other words, since light emitted from the LEDs is dispersed in a conical shape, the incident surface of the light guide member and the LED array is not parallel. As a result, when for example the interval between the incident surface of the light guide member and the LEDs is different on both ends in the main scanning direction, the light amount of light that is incident upon the light guide member is high in portions in which the interval is small, and the light amount is low in portions in which the interval is large. Consequently, a dotted pattern may be produced.
Furthermore, even when the incident surface of the light guide member is parallel to the LED array, if the interval between the LEDs and the incident surface of the light guide member is excessively large, the light amount of light that is emitted from the LEDs and becomes incident upon the light guide member is reduced, and therefore, may result in insufficient luminance on the document surface.
As a result, an image forming apparatus is provided in which the light guide member protrudes towards the plurality of LEDs arrayed in a linear configuration, and thereby determines the positional relationship between the LEDs and the light guide member, and uses a fixing member such as a screw or the like to fix the respective components in a fixed positional state.
However, in this image reading apparatus, when the light guide member is pressed onto the LEDs during assembly operations, it may be the case that a deviation is caused in the positional relationship between the light guide member and the LEDs due to a frictional force produced when fixing with a fixing member such as a screw or the like.
For this reason, an operator must secure and fix these components in a state in which the light guide member is pressed onto the plurality of LEDs.
Therefore, a pressing force is applied during assembly operations to the plurality of LEDs, and even after securing, a state is maintained in which a pressing force is applied.
As a result, during assembly operations, it may be the case that the LEDs are damaged, or that mounting detachment is produced in which the LEDs are detached from the LED array substrate. Furthermore, since a pressing force is applied to the LEDs even after assembly operations, it may be the case that damage to the LEDs or detaching of the mounting will result from slight impacts such as a vibration during use or during transporting.